(Fluoroorgano)fluoroboranes and -fluoroborates I: synthesis and spectroscopic characterization of potassium fluoroaryltrifluoroborates and fluoroaryldifluoroboranes

A convenient preparation of K[ArBF3] (Ar= 2-C6H4F, 3-C6H4F, 4-C6H4F, 2,6-C6H3F2, 3,5-C6H3F2, 2,4,6-C6H2F3, 3,4,5-C6H2F3, 2,3,4,5-C6HF4 and C6F5) is offered and the IR and multinuclear NMR spectra of these salts are reported. Treatment of the trifluoroborate salts with BF3 in chlorocarbon solvents provides an easy synthetic route to the corresponding aryldifluoroboranes ArBF2. The multinuclear NMR spectra of ArBF2 are presented. The electron substituent effect of the [-BF3](-)-group shows this substituent as one of the strongest sigma-electron donors, while its pi-electron influence is negligible (sigma(I) = - 0.32, sigma(R) = - 0.07). (C) 2000 Elsevier Science S.A. All rights reserved.